The invention relates to a device for enabling a doctor or other skilled operator to obtain correct pressure readings of a tonometer.
About one hundred and fifty years ago the increase of eye pressure was found to be related to glaucoma, a disease with high index of blindness. It was not until the beginning of the 19th century that the first excellent description of glaucoma with raised ocular tension was given by Antoine Demours. He noticed that "le globe oculaire devient dur au toucher" (Duke Elder-System of Ophthalmology--vol. XL--1969).
With this observation, the first method of verifying ocular pressure appeared, which was effected by depression of the eye by the fingers of the examiner. This method, in use until today, is not precise and does not offer reliable means of information.
In 1905 Schiotz discovered the mechanical tonometer bearing his name. It is able to reveal in millimeters of mercury the pressure encountered. However, the mobility of the eye does not permit that repeated pressure readings in the course of the diagnosis or treatment of the glaucoma be carried out under equal conditions of the eye, as scientific research demands, giving rise to different interpretations among researchers.
The present invention complements pressure readings by the Schiotz tonometer, which can be carried out in one and the same eye and can be registered for subsequent comparison.
This invention offers tranquility to the patient who does not feel nor percieve the taking of the pressure; it facilitates also the technique of the physician, assuring scientific rigor in the research. Other tonometers have been submitted, like those of Gradle, McLean Sunter, Harrington, Goldman, Lichtenstein and others, --all of them with the object of discovering minimum pressures in the course of a beginning glaucoma. On the other hand, the inaccuracy of the results obtained have been connected with variable resistance of the ocular globe to the depressing force of the tonometer. In 1939 Friedenwald used a mathematical formula based on the depressing force of the cornea, the depression area, ocular rigidity, cornea identation, and founded the method of simple differential tonometry. In 1959 Goldman created his Applanation Tonometer ("Tonometro de Aplanacao"), reducing the depression area of the cornea to a diameter of 3.06 mm, with 200 Micrometers of cornean indentation. In 1967, Lichtenstein, using acoustic energy reduced the indentation of the cornea to 2.5 micrometers. These outstanding researchers, by employing the method of ocular depression with the aid of mechanical means (original discovery of Schiotz), made use of mathematical calculations applied to biological processes, which led to disagreement in the interpretation of the results. "The computation is a good example of difficulty and danger of expressing biological processes in terms of mathemetical equations with their deceptive aura of accuracy"--Duke Elder--System of Ophthalmology--vol. XL--1969.
Reverting to the first studies of Schiotz, the present inventor tried to give more precision and scientific accuracy to the reading of ocular pressure by the tonometer of Schiotz, to map the results by degrees, to connect them by causes and effects, deducting and concluding. He followed the inductive method of experimental science--instead of the mathematical demonstrative method. Hence, this invention of the principle of registration of the position of the eye examined during repeated pressure readings which readings are to be related, creates a valuable instrument for experimental science.
The object of this invention is to provide a method and an apparatus to complement the reading of ocular pressure by the tonometer of Schiotz or similar ones. Other objects are to allow for measurement with entire comfort of the examined person, which latter does not feel nor perceive the mechanical contact with the cornea. A principle of this invention is to register the position of the eye, when pressue is taken, by the Schiotz method of ocular depression or similar ones, whereby a physical system immobilizes the eye under examination.
The fixation reflex of the eyes is maintained by the center of psycho-motive reflexes. It coordinates the ocular muscles moving the two eyes as if they were just one eye. The excitation of the retina of the fixing eye brings about the mechanism of association of the two eyes in a certain position, maintaining the examined eye immovable. This position can vary in vertical, horizontal, oblique and rotating direction thanks to an extremely delicate motive mechanism directed by will power. Thus, while the patient immovably fixes a given point in space (for instance the ceiling of the examination room) through the central hole of the cone, the other eye, which is being examined, also remains immovable by virtue of the fixation reflex. Once an adequate position has been arrived at by movements in the cone around the control system of eye movement, and when the desired position of the eye has been reached, ocular pressure is measured by the tonometer of Schiotz and the position of the eye is registered.
The objects of the invention are attained by providing a head piece adapted to fit on the forehead above the eyes, to which headpiece is attached a hollow cone open at both ends, the position of the cone being adjustable so that its area extends at various angles in a direction away from the eye with the larger opening of the cone nearest the eye, whereby, depending on the position of the cone, the eye can view a point or small area defined by the smaller opening in the cone. Preferably the cone is adjustable laterally to be positioned in front of either the right or the left eye and is also pivotable in a horizontal as well as in a vertical direction to fix the eye in a variety of positions. Once the position of one eye is fixed by the cone, the other eye is also fixed in a corresponding position and the tonometer reading is taken on said other eye.